1. Field of the Invention
The present invention relates to transferring papers for use in electrophotography wherein electrostatic latent images are developed by a liquid developer and the images thus formed are transferred to a transferring paper to obtain copied images. More particularly, the present invention relates to transferring papers, in particular, useful in electrophotography wherein images developed by a liquid developer are transferred in the presence of a liquid carrier by electrophoresis.
2. Description of the Prior Art
A number of electrophotographic processes such as Carlson process, Photovoltaic process, Smoke printing process, Persistent internal polarization process, Electrolytic electrophotography, Canon NP process, electrophoretic electrophotography, and the like are well known in the art and it is also known to one skilled in the art that the images formed by the above processes are transferred or that the electrostatic latent image formed are made visible by a liquid developer and then transferred to a transferring paper to obtain permanent printed copies.
Generally, in a wet-development, the latent image is made visible using a liquid developer which is prepared by dispersing toners in an insulating liquid and the image thus developed is then transferred in an extremely short period of time by electrophoresis by bringing a carrier liquid film on a photosensitive plate in contact with a transferring paper. In case that a visible image is formed in a liquid film as in Electrophoretic electrophotography, the image is transferred by electrophoresis during the short period of time while the liquid film is in contact with the transferring paper.
However, if usual papers are used as the transferring paper, the paper absorbs the carrier liquid during the short contact period of time and thus the carrier liquid film cannot be maintained. Therefore, the electrophoresis of toner is prevented and the transferring efficiency is considerably lowered and, as a result, the transferred image is disturbed.
Where a large amount of the carrier liquid remains on the photosensitive plate, the transferability of toner image is increased but, however, the transferring paper is unnecessarily wetted, whereby a long time is undesirably needed at the drying stage. In addition, a large amount of carrier vapor is formed, which is not desired from a hygienic point of view.
Furthermore, if the paper absorbs a large amount of carrier liquid, wettability of the photosensitive plate or the electrode is lowered and therefore cleaning thereof becomes difficult, and sometimes they are damaged.
Accordingly, it is necessary to lower oil absorbant properties of the transferring paper and to improve hold out thereof so as to depress the absorption of the carrier liquid and so as to maintain the carrier liquid film during the contact period of time while the transferring paper is in contact with the photosensitive plate or electrode.
A typical method of imparting oil resistance to paper and depressing oil absorptivity thereof is to form an oil repellent, i.e. high hydrophilic polymer film on the surface of paper or to impregnate the paper with such a polymer. Polyvinyl alcohol, cellulose derivatives, salts of hydrophilic group containing polymers, water soluble natural polymers, and the like are used for coating, impregnation, and compounding. Although oil resistance of paper is improved and oil absorptivity thereof is decreased by using the foregoing polymers, the paper so prepared is insufficiently dried at the paper machine or coating machine due to high film forming properties of such polymers. Furthermore, the paper formed has defects in that the paper tends to curl and the oil resistant film is readily cracked during calendar processing. The paper is sensitive to moisture due to high hydrophilic properties thereof. Since the binding strength of the paper with a developer is poor, the formed image is undesirably removed.